1. Field of the Invention
The invention relates to a cylindrical mount for optical components of a variable-power objective.
2. Related Art
Many versions of mounts for variable-power objectives, such as zoom lenses, are known. In them, a plurality of lenses or lens groups are held in different carriers and are displaced relative to one another along the optical axis of the objective in order to change the focal length. Thus, in variable-power (or zoom) objectives, a change in focal length of the objective results in variable magnification of the object in the image plane.
In addition, it is often necessary to displace individual lenses or lens groups in order to set the focus of the objective, which is independent of changing the focal length. A zoom objective in a position of a selected focal length setting should be adjusted or focussed to the correct distance of the object for sharp imaging in the image plane.
As may be gathered, for example, from U.S. Pat. No. 5,675,444, the displacement of the lenses or lens groups relative to one another normally takes place via a cam control which is driven by an outer rotary ring. In this case, the carrier of the lenses or lens groups engages via a pin into the cam track of a rotatably mounted cam carrier and is simultaneously guided in the axial direction in a straight-line guide. U.S. Pat. No. 5,748,390 discloses rod systems for guidance in a straight line, on which the lens carriers run and which are fastened to the mount. Further rod systems may also be fastened to one of the adjustable lens carriers. This ensures that, in the event of displacement, the lenses are not rotated, so as to avoid optical imaging errors due to decentering. It is also known to separate the cam control and the straight-line guide from one another, in which case separate straight-line guide elements for the carriers of the lenses are provided in the mount cylinder.
In the known mounts, the focus setting movement is transmitted via a helical gearing, in which the mount of the lenses or lens components to be displaced is rotated. Depending on the pitch of the driving worm, the angle of rotation is generally not too great, so that any possible imaging errors due to the rotation of the optical surfaces relative to the fixed lens surfaces are often acceptable. However, for example, some sluggishness in the movement of the worm is unavoidable.
Front lens groups, onto which filters and diaphragms are also attached, are frequently used for focussing. In order to use polarizing filters and noncircular diaphragms, it is then necessary to choose a different type of fastening, so that their orientation can be maintained when the focus is being set.